Lecture 5 Flashcards
What are the two steps of gene expression?
transcription and translation
What is transcription?
Reading a DNA template to make an RNA copy
What is translation?
Decoding RNA to assemble a protein.
True or False: transcription and translation are coupled in prokaryotes.
True
What is RNA polymerase?
A complex enzyme that carries out transcription by making RNA copies (called transcripts) of a DNA template strand
What is a sigma factor?
Guides the core RNA polymerase to the promoter.
How many RNA polymerases do prokaryotes have?
One
How many RNA polymerases do eukaryotes have?
Multiple (Pol I- Pol V)
Archaeal RNA polymerases and transcription factors are more similar to _______________.
eukaryotes
True or False: Every cell has a ‘housekeeping’ sigma factor.
True
What is the sigma factor in E.coli?
sigma^70
Which consensus sequences does the sigma factor recognize?
-10 & -35 regions relative to the start site of transcription (start site= +1)
True or false: A single bacterial species can make several different sigma factors.
True
What is the function of the ‘housekeeping’ sigma factor?
It serves routine transcription duties
What is the function of ‘alternative’ sigma factors?
Genes that serve a specialized function
True or False: Mutations in the consensus sequence can affect the strength of the promoter.
True
What are the three phases of transcription?
- Initiation
- Elongation
- Termination
What is the initiation phase of transcription?
RNA Pol holoenzyme binds to the promoter
What is the elongation phase of transcription?
Sequential addition of ribonucleotides from nucleoside triphosphates
What is the termination phase of transcription?
RNA Pol detaches from DNA, after the transcript is made.
RNA holoenzyme forms a loosely bound, _______________ with DNA during initiation.
closed complex
The closed complex must become a ______________ through the unwinding of one helical turn.
open complex
RNA polymerase becomes _______________ to DNA, and so begins transcription.
tightly bound
What is typically the first ribonucleoside triphosphate of the new RNA chain?
A purine (A or G)
True or False: The sigma factor leaves the complex after transcription is initiated?
True
How fast does RNA polymerase move along the template?
45 bases/sec
What complex is formed when the DNA is unwound further ahead of the complex?
17-bp transcription bubble
Positive supercoils are removed by what?
DNA topoisomerases
What are the two known termination signals/mechanisms in bacteria?
Rho-Dependent & Rho-Independet
In Rho-dependent termination:
- Rho binds to C-rich regions
- RNA is threaded through Rho hexamer, pulling Rho towards RNA polymerase
- Contact between Rho and RNA polymerase leads to termination
In Rho-independent termination:
contact between hairpin NusA protein and RNA pol causes termination
What two fundamental criteria must antibiotics meet?
- They must grow or retard the growth of a pathogen
- Must not harm the host (its selective)
What is Rifamycin B?
- Selectively binds to the bacterial RNA pol
- Inhibits transcription initiation
What is Actinomycin D?
- Nonselectively binds to DNA
- Inhibits transcription elongation
What does Rifamycin B bind to?
Beta subunit of RNA Pol
What is Rifamycin B effective against?
Mycobacterium
True or False: Rifamycin B is naturally produced by amacolatopsis rifamycinia.
True
How does actinomycin D inhibit transcription elongation?
Phenoxazone rings nonspecifically intercalate into DNA between base stacks
Do the side chains of actinomycin D wrap around the major or minor groove?
minor groove
True or False: Actinomycin D has been used to treat cancer.
True
What are the consensus sequences of sigma^70?
TTGACAT (-35), TATAAT(-10)
In archea, is translation initiation similar to that of bacteria or eukaryotes?
Similar to bacteria
In bacteria, is the size of the ribosome similar to that of archea or eukaryotes?
Similar to archea
In archea, is the chemical sensitivity of ribosomes similar to that of bacteria or eukaryotes?
Similar to eukaryotes
True or False: Even though the ribosomes found in archea are similar to eukaryotes, the eukaryotic cells have larger and more complex ribosomes.
True
True or False: Bacteria use a complex set of transcription factors.
False
True or False: Bacteria is sensitive to chemical inhibitors.
True
True or False: The sigma factor, RpoD^70 is recognized in most genes.
True
How is RpoD^32 recognized?
In heat-shocked genes
Where is RopF^28 recognized?
Recognized in genes for chemotaxis/motility
Where is RopS^38 recognized?
In stationary and response genes
Where is RpoN^54 recognized?
In genes responsible for nitrogen metabolism
